The present invention relates to compositions and methods of combining a water-in-oil emulsion polymer with an aqueous saline well treating fluid without coagulation of the polymer.
Aqueous saline well treating fluids are used in a variety of operations and treatments in oil and gas wells. Such operations and treatments include, but are not limited to, well completion operations, production stimulation treatments, formation permeability conformance control treatments, and treatments to reduce undesirable well bore fluid inflows and outflows.
An example of a well completion operation is primary cementing. In a primary cementing operation, a string of pipe such as casing or a liner is cemented in a well bore. In performing primary cementing, a cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe string in the well bore and bonds the exterior surfaces of the pipe string to walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented.
Another example of a well completion operation that involves the use of a viscous aqueous saline treating fluid is gravel packing. In gravel packing operations, solid gravel particles such as sand are carried to a subterranean zone in which a gravel pack is to be placed by a viscous gelled treating fluid, often a viscous gelled aqueous saline treating fluid. That is, the gravel pack is suspended in the viscous treating fluid at the surface and carried to the subterranean zone in which the gravel pack is to be placed. Once the gravel is placed in the zone, the high viscosity gelled aqueous treating fluid is broken (the viscosity is reduced) and recovered (returned to the surface). The gravel pack produced functions as a filter to separate formation solids from produced fluids while permitting the produced fluids to flow into and through the well bore.
An example of a production stimulation treatment utilizing a viscous gelled aqueous treating fluid is hydraulic fracturing. That is, the viscous treating fluid, referred to in the art as a fracturing fluid, is pumped through the well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended into the subterranean zone. The fracturing fluid also carries particulate proppant material, e.g., sand, into the fractures. The proppant material is suspended-in the viscous treating fluid so that the proppant material is deposited in the fractures when the viscous fracturing fluid is broken and recovered. The proppant material functions to prevent the formed fractures from closing whereby conductive channels are formed through which produced fluids can flow to the well bore.
An example of a formation permeability conformance control treatment involves enhanced recovery techniques such as water flooding. In water flooding, an aqueous displacement fluid is injected under pressure into an oil containing subterranean formation by way of one or more injection wells. The flow of the aqueous fluid through the formation displaces oil contained therein and drives it to one or more producing wells. Prior to injecting the displacement fluid into the subterranean formation, the permeability of the subterranean flow passages having high permeability and low oil content is reduced. This is accomplished by injecting aqueous solutions, often aqueous saline solutions containing polymers into the high permeability flow passages whereby the polymers are gelled and cross-linked therein.
An example of a treatment to reduce undesirable well bore fluid inflows and outflows involves the production of oil and/or gas from formations containing permeable channels therein through which inflows or outflows occur. For example, when an oil-bearing formation contains highly, permeable water channels communicating the well with water zones, undesirable water enters the well. In order to plug the channels, polymers have been introduced into the water channels wherein the polymers are cross-linked so that the water channels are plugged.
In onshore wells and offshore platform wells, polymer additives to be utilized in aqueous treating fluids are transported to the well location in liquid-form. Examples of the polymer additives utilized include, but are not limited to, fluid loss control additives, viscosity increasing gelling agents, dispersants, cement set retarders and the like. However, because many of the polymer additives form extremely viscous solutions in small concentrations of water, large volumes of the polymer additive solutions in small additive concentrations are required to perform a well treatment.
Many of the well treating fluid polymer additives are synthesized as water-in-oil emulsions that contain high quantities of the polymer (referred to herein as “water-in-oil emulsion polymers”). However, when the water-in-oil emulsion polymer additives are combined with an aqueous saline fluid, the polymers immediately form precipitates which coagulate in the saline fluid.
Thus, there is a need for a method of combining a water-in-oil emulsion polymer additive with an aqueous saline well treating fluid without precipitation and coagulation of the polymer additive in the fluid.